Electrically powered vehicles require electric motors that are simple, safe, highly efficient and provide good performance. Electric motors generally fall into one of two types, those with a high operating voltage and those with a low operating voltage (typically 50 V or less). High voltage electric motors clearly pose a greater risk of electric shock to people and animals when used in a vehicle and are thus subject to stringent safety requirements, which render them a complex and consequently high cost solution. In order to provide the same power, low-voltage motors require a higher operating current, since power is the product of current and voltage. However, operating conventional low voltage three-phase electric motors with high winding currents poses several problems including the need for larger cables and connectors a more complex controller for high current switching, larger capacitance requirements and low inductance. In addition, the heat losses or copper losses (coil resistance×coil current squared), due to the resistance of the windings become significant.
WO 2004073157 describes a low-voltage electric motor with distributed winding intended to address this problem. In this motor the total current is distributed across several coils or windings which significantly reduce the winding current. However, each coil is controlled separately which requires a complex controller with a large amount of electronics. A low voltage in-wheel three-phase electric motor is also described in GB2462940A. This motor has a number of independently controlled coil sets distributed around the stator. Each coil set is made up of three coil sub-sets, where each coil sub-set is driven at a different phase. However, the same three phases are used in each coil set. This arrangement provides some simplification over the disclosure of WO 2004073157, however, the controller is still complex as it requires an independent CPU controller for each coil set.
Thus, while it is known to provide low voltage and high current electric motors, there is a need to provide such motors in a simple and cost effective way that does not compromise on high performance.